Design study of a rocket-borne free-flow aerosol collector for supersonic speed deployment by means of numerical efficiency analyzes

Abstract. The ice nuclei on which the cloud particles of mesospheric ice clouds, i.e. noctilucent clouds (NLC), form are largely unknown. Since in-situ measurements within NLC in about 85 km altitude are only possible by using sounding rockets, the careful design of an instrument to be deployed on board of the rocket is crucial. This study investigates the development of an inertia-based particle collector, which allows for sampling NLC particles during a sounding rocket flight for off-line single particle physico-chemical analyzes. Computational fluid dynamics (CFD) simulations support the design and development process in reference to a basic mechanical concept of particle sampling and sample storage, which is also presented here. Numerical studies of the supersonic flow field (Mach numbers 1.31 and 1.75) around the instrument module on the sounding rocket are carried out at different flow velocities (i.e. 300 m s⁻¹ and 400 m s⁻¹) and angles of attack (i.e., at +30°, 0° and −30°) for optimizing the aerodynamic design, arrangement, and orientation of the particle collectors. Thereby, the localization and extent of the occurring shock wave is investigated and the thickness of the boundary layer around the instrument module is determined to prevent the impairment of the particle sampling. Simulated particle trajectories based on particle radii of 0.6 nm at the lower limit of conceivable particle sizes confirm possible impactions on the collector surfaces. The investigations confirm the effectiveness of the designated particle collectors and render a yet pending rocket flight a valuable option in the investigation on the morphology, chemical composition, size, and number concentration of NLC particles and their nucleating particles.